Hi Walt,
Sugar inhibits gluten formation, so when you have an excess of sugar, your cake will have less bread-like characteristics and be more fluffy, tender, and soft. The sugar and gluten have an impact on the crumb.
Cake mix cakes tend to have more leavener in them, and are made with more liquid and more fat (since they call for oil instead of butter), and it creates a more spongy texture. The water opens up the crum through evaporation, along with the chemical leaveners that react, and it creates a very open texture. This eggless chocolate cake is a homemade version of a cake mix cake. And the texture is quite different from a cake that uses the creaming method with butter.
You are right about the type of flour having an impact. Cake mixes may rely on flours that are higher in starch and lower in protein, which also would create a lighter texture.

Hi Lekie,

Most cake recipes use the creaming method, as detailed above, where you first mix butter and sugar to incorporate air into the butter, then add the eggs, and then the dry ingredients. But it really depends on the recipe. Ideally, you would follow a recipe from a reputable site or cookbook that will tell you what ingredients to mix together and in which order. Hope that helps!

Hi Denyse, for a sponge cake where eggs are whipped with sugar, it is better that the sugar dissolves before proceeding with the dry ingredients. Otherwise, there may be a crystallized layer on the outside of the cake, or the sugar may draw out moisture later as it bakes, leading to textural imperfections. It doesn't always happen, but it can!

As for cake sinking, are you sure the cake is fully baked? Does it sink as it cools? Some sponge cakes are cooled upside down so that they don't collapse (like the Angel food cakes, for example). Otherwise, there are many reasons cakes collapse. Here is an article about it: https://bakeschool.com/cake-collapse/

That's so interesting! I think you are right and that in many cases, the mixing methods lead to slight variations that most people won't notice except for the baker. Whatever method is easiest or works best for you is definitely the way to go! Thanks for your comment!